Joint compound composition for building elements and method of producing a structure

ABSTRACT

The present invention relates to a joint compound composition for building elements, particularly paper-faced plasterboards. 
     This composition comprises:
         a) 50 to 60% of calcium sulphate hemihydrate;   b) 5 to 15% of an organic binder in powder form; and   c) 0.05 to 0.2% of a water repellent.       

     The invention also relates to a method producing a structure, such as a partition, a wall trim or a ceiling. 
     According to this method:
         building elements are juxtaposed;   the joint compound composition according to the invention is mixed with water so as to obtain a joint compound;   the space between the building elements is filled by means of the joint compound obtained above, without using a tape; and   the joint compound is left to harden.

The present invention relates to a joint compound composition forbuilding elements, particularly paper-faced plasterboards, and to amethod of producing a structure such as a partition, a wall trim or aceiling.

It is well known to use building panels such as plasterboards forproducing partitions and trims for vertical or inclined elements or forproducing suspended or non-suspended ceilings.

These plasterboards are generally formed from a core, essentially madeof plaster, covered on each of its faces with a sheet serving both asreinforcement and as facing, which sheet may be formed from paper orfrom inorganic fibres.

European Patent Application published under the number 496 682 disclosesa joint compound for filling the joints formed by the contiguous lateraledges of two plasterboards and for forming a tapeless joint. This jointcompound comprises, in percentages by weight calculated with respect toall of the dry matter:

-   -   5 to 30% of hemihydrate plaster;    -   7 to 25% of polymer as a suspension in an aqueous phase and/or        as a redispersible powder;    -   if necessary, other additives for adjusting the setting time        and/or for adjusting the quality of the paste and/or the        adhesion of the joint compound; and    -   at least one inner filler in an amount making up the composition        to 100%.

Example 15 of that patent application discloses in particular acomposition comprising, in parts by weight:

-   -   194 parts of alpha-plaster;    -   108 parts of a vinyl acetate/ethylene copolymer stabilized with        polyvinyl alcohol and having a solids content of 55%;    -   6.6 parts of a vinyl acetate/ethylene copolymer as a        redispersible powder;    -   0.67 parts of cellulose ether;    -   669.3 parts of limestone    -   2.25 parts of polyvinyl alcohol;    -   0.027 parts of polyacrylamide;    -   2.25 parts of clay;    -   0.045 parts of white Portland cement;    -   1.12 parts of gypsum+starch (50/50); and    -   0.125 parts of hydrolytically degraded keratin.

U.S. Pat. No. 5,653,797 discloses a composition for filling the jointsformed by the adjacent edges of panels formed from plasterboards, thiscomposition comprising:

(a) calcium sulphate hemihydrate;

(b) water in an amount sufficient to adjust the viscosity of thecomposition;

(c) a set retarder comprising a composition based on a polymercomprising acrylamide and acrylic acid monomers; and

(d) a set accelerator comprising a metal salt comprising acid cations.

That patent mentions the possible use of a binder such as a latex orpolyvinyl alcohol.

Table II of column 8 of that patent indicates a composition comprising:

-   -   20 to 30% of calcium sulphate hemihydrate;    -   1 to 4% of a latex-type binder;    -   1 to 10% of perlite;    -   10 to 50% of limestone;    -   0.5 to 4% of clay;    -   0.1 to 1% of a thickener;    -   0.5 to 3% of talc;    -   1 to 4% of mica;    -   0.01 to 1% of the particular retarder described above;    -   0.01 to 2% of the particular accelerator described above;    -   0.01 to 1% of a preservative; and    -   20 to 30% of water.

However, when this composition hardens, it undergoes excessiveshrinkage.

International Application published under the number WO 99/48833discloses a composition that can be used for filling joints betweenadjacent plasterboards. This composition causes hydraulic setting whenit is mixed with an effective amount of a set accelerator and itcomprises a material such as plaster and a particular retarder based ona sulphonated polymer or copolymer.

Example 11 of that application discloses a composition for fillingjoints having the following formulation (in % by weight):

-   -   35.9% of calcium sulphate hemihydrate;    -   4.1% of a vinyl acetate/ethylene copolymer, in 50% water;    -   7.1% of perlite;    -   0.3% of cellulose ether;    -   8.1% of limestone;    -   2.6% of wollastonite;    -   2.6% of kaolin;    -   0.1% of lime;    -   1.0% of retarder; and    -   38.3% of water.

This composition also has the major drawback of resulting in excessiveshrinkage.

The joint compounds or compositions that have been described have thedrawback of being unsatisfactory because they do not have all thefollowing qualities taken together:

-   -   good workability;    -   a colour compatible with that of the building elements for which        they are intended; and    -   the ability to obtain a joint having zero or almost zero        shrinkage and good mechanical properties (hardness, tensile        strength, compressive strength, impact strength, and slight        deformability or elasticity in order to prevent cracking).

Furthermore, the compositions of the aforementioned documents U.S. Pat.No. 5,653,797 and WO 99/48833 have the particular feature of containinga powerful retarder that blocks the hydration of the calcium sulphatehemihydrate. It is therefore the user who adds an accelerator in orderfor this hydration to start. This entails difficulties when the jointcompound is being used on a work site, since there is a risk of the usernot adding the correct dose of accelerator.

In addition, these compositions change over time. Depending on the timethat has elapsed since the preparation of the composition, the sameamount of accelerator added at the moment of application does not havethe same effects. It follows that there is uncertainty as regards thehydraulic setting in the sense that it is not possible to know preciselywhen this setting will take place.

Moreover, other problems arise when the building element is aplasterboard covered with a paper facing:

-   -   it is necessary, on the one hand, for the joint compound to have        good adhesion to the paper facing and, on the other hand, for        the adhesion of a wallpaper to the joint to be also good but not        excessive, so as to make it possible to strip wallpaper one or        more times without either tearing or degrading the joint        compound; and    -   the joint compound must have a water and/or paint absorption as        close as possible to that of the facing paper, so as to avoid        having to apply a coat of primer before wallpapering or        painting.

The aim of the invention is therefore to provide a tapeless jointcompound composition which, after mixing with water, gives a jointcompound that has the abovementioned qualities and characteristics. Itis based on the discovery that, in order for a joint compound to besatisfactory, it is necessary for it to contain calcium sulphate, abinder and a water repellent, and to do so in well-defined proportions.

Thus, the subject of the invention is a joint compound compositioncomprising:

a) 50 to 60% of calcium sulphate hemihydrate;

b) 5 to 15% of an organic binder in powder form; and

c) 0.05 to 0.2% of a water repellent.

Such a composition, after mixing with water, therefore gives a hydraulicsetting joint compound that can be used by itself, that is to say it isboth a filling joint compound and a finishing joint compound, and makesit possible to produce a joint without having to use a tape.

The subject of the invention is also a method of producing a structure,in which:

-   -   building elements are juxtaposed;    -   the joint compound composition according to the invention is        mixed with water so as to obtain a joint compound;    -   the space between the building elements is filled by means of        the joint compound obtained above, without using a tape; and    -   the joint compound is left to harden.

Finally, the invention relates to a joint as obtained by implementingthis method.

Other features and advantages of the invention will become apparent onreading the following description.

DETAILED DESCRIPTION OF THE INVENTION

Composition According to the Invention

The general composition of the invention was given above.

According to a preferred embodiment of the invention, the compositionfurthermore includes:

d) from 1 to 10% of a lightening agent (light weight agent)

According to one particularly advantageous embodiment of the invention,the composition comprises:

a) 50 to 60% of calcium sulphate hemihydrate;

b) 5 to 10% of an organic binder;

c) 0.07 to 0.15% of a water repellent; and

d) 3 to 7% of a lightening agent.

Of course, the balance to 100% consists of one or more fillers andoptionally one or more additives chosen from water retainers,thickeners, workability agents, dyes or pigments, set retarders and setaccelerators.

Preferably, a calcium sulphate hemihydrate of the alpha type is usedsince this allows the necessary amount of water for mixing thecomposition to be reduced.

The organic binder has the function of softening the calcium sulphate inthe joint and of obtaining good mechanical properties. As binder, it ispossible to use copolymers of vinyl esters and of ethylene monomers,such as ethylene/vinyl acetate (EVA) copolymers, whether plasticized orunplasticized, ethylene/vinyl versatate copolymers and vinylacetate/vinyl versatate copolymers, polyacrylics, vinyl acetate/acryliccopolymers, styrene/acrylic and styrene/butadiene copolymers, vinylacetate/vinyl versatate/acrylic and vinyl acetate/vinyl versatate/vinylmaleate terpolymers, acrylic terpolymers and blends thereof.

The vinyl copolymers may be stabilized with polyvinyl alcohol.

The organic binder is also preferably used in the form of aredispersible powder.

As water repellent that can be used in the joint compound compositionaccording to the invention, it is possible to choose, in particular, afatty acid, a fatty acid salt, a wax or a silicone derivative.

Preferably, oleic acid or stearic acid are used as fatty acid.

As fatty acid salt, alkali metal or alkaline-earth metal salts arepreferred, particularly sodium, potassium, magnesium or calcium salts.

As silicone derivative, mention may be made of siliconates, silanes,hydrogenated silicone oils, silicone emulsions, amino siliconeemulsions, alkylsiloxane resins, such as hydrogenomethylpolysiloxane andpolydimethylaminosiloxane, and blends thereof.

The water repellent most particularly preferred is chosen from oleicacid, stearic acid, sodium oleate and sodium stearate.

As lightening agent suitable for the invention, mention may be made ofperlite, glass microbeads and polymer microspheres.

Preferably, the lightening agent is non-water-repellent expandedperlite.

It is also possible to use at least one filler such as, for example,limestone, magnesium carbonate, calcium magnesium carbonate (dolomite),magnesium hydroxide, silica, natural or synthetic gypsum, or else groundnatural or synthetic anhydrite. Preferably, limestone is used.

The joint compound composition according to the invention may alsoinclude one or more water retainers that may be chosen from celluloseethers, particularly methyl cellulose (MC), carboxymethyl cellulose(CMC), hydroxyethyl cellulose (HEC), ethylhydroxyethyl cellulose (EHEC),methylhydroxypropyl cellulose (MHPC) and methylhydroxyethyl cellulose(MHEC).

These water retainers may also have a viscosity-modifying action andtherefore have a positive influence on the quality of the paste.

Optionally, the cellulose ethers may be partly substituted with or elseaccompanied by naturally occurring polycarbohydrate derivatives thatparticipate in the rheology of the paste, such as galactomanans,polysaccharides, xanthan, guar derivatives, etc. The commerciallyavailable “modified” cellulose ethers are often the aforementionedmolecules with other wetting agents or thickeners: they may be highlysuitable for the invention. However, it is possible to use otherwater-retaining or viscosity-modifying agents, such as starch ethers oragents which, in addition to their main function, exhibit a sufficientwater-retaining action, such as polyvinyl alcohol.

The joint compound composition according to the invention mayfurthermore include one or more thickeners, which may bepolyacrylamides, CMC, starch derivatives, or clays such as attapulgite,sepiolite, montmorillonite and bentonite.

Preferably, the thickener is a polyacrylamide.

The composition according to the invention may also include one or moreworkability agents. This workability agent may be a plasticizer, awetting agent or a slip agent.

As plasticizer suitable for the invention, mention may be made ofsulphonated polymers, preferably agents based on sulphonatedmelamine-formaldehyde.

As wetting agent suitable for the invention, mention may be made ofalkyl sulphates, such as sodium lauryl sulphate, alkylaryl sulphonatesor phosphate derivatives.

As slip agent suitable for the invention, mention may be made of talc ormica. Because of their lamellar morphologies, these agents promote slipof the spreader when jointing and help to reduce shrinkage.

The composition according to the invention may also contain one or morecolorants that may be chosen, for example, from titanium dioxide andoptical brighteners.

The composition according to the invention may also contain additivesfor adjusting the setting time, these being set retarders or setaccelerators.

In general, a pair of agents, one of which is an accelerator and theother a retarder, is added.

Among set accelerators that may be suitable for the invention, mentionmay be made of sulphates. Preferably, gypsum is used in the form of apowdered mixture of gypsum and starch, the gypsum always retaining thesame ability to accelerate the setting of the plaster thanks to thestarch, which preserves it from ageing. Thus, the setting of the jointcompound is made insensitive to external gypsum contaminations,especially those that may be present in the form of setting nuclei inthe plasterer's trough or applicator.

Among set retarders, mention may be made of agents based onhydrolytically degraded keratin, hydroxycarboxylic acids, such astartaric acid and citric acid, salts of these acids, and calciummonophosphate. These agents may be employed in proportions that varyaccording to the proportions of hemihydrate plaster and of accelerator.

Advantageously, the proportions of accelerator and of retarder areadjusted in such a way that the hardening time is short enough to allowthe jointing to be completed during the day.

Various other additives may optionally be added to the compositionaccording to the invention. Thus, it is possible to add to thecomposition an agent capable of bringing the pH of the joint compound toa basic pH. The basic agent makes it easier for the water-retainingagent, mainly when it is cellulose ether, to dissolve and consequentlyfavours build-up of viscosity. As basic agent, an inorganic agent may beused, preferably “white” Portland cement, that is to say Portland cementdevoid of iron oxide, or lime.

Also preferably, the amount of basic agent needed to achieve a pH ofgreater than or equal to 8 is introduced into the joint compound.

Preparation of the Composition According to the Invention

The joint compound composition according to the invention is prepared byblending its constituents in any order, preferably until a homogeneouspowder is obtained.

Although the constituents of the composition according to the inventionare not necessarily all in powder form, once they have been blended thecomposition according to the invention is generally and overall in theform of a powder.

In general, the particles making up the powder have a diameter of atmost 200 microns.

Method of Producing a Structure According to the Invention

According to the invention, to produce a structure, panels or buildingelements are juxtaposed, the joint compound composition according to theinvention is mixed with water, so as to obtain a joint compound, andthen the space between the building elements is filled by means of thejoint compound obtained, without using a tape, and the joint compound isleft to harden.

The mixing is generally carried out with a mass ratio of water to jointcompound composition ranging from 40 to 50%.

The method according to the invention applies in particular to theproduction of a structure by means of plasterboards coated with a paperfacing.

These plasterboards may have edges of various geometries, and inparticular feathered, rounded or both rounded and feathered edges.

Joint According to the Invention

By implementing the method according to the invention, it is thereforepossible to obtain a satisfactory joint.

Such a joint also has the advantage of allowing the application ofpaint, by all suitable painting techniques used by those skilled in theart, particularly by applying the paint with a roller, a brush or byairless spraying.

EXAMPLES

The following examples illustrate the present invention without,however, limiting the scope thereof.

Example 1

A joint compound composition E according to the invention was prepared,together with three joint compound compositions in powder form, A, B andC, outside the scope of the invention, by way of comparison.

The corresponding formulations are given in the following table, inwhich the values indicated correspond to parts by weight:

JOINT COMPOUND A B C Composition E (inv.) (comp.) (comp.) (comp.)Plaster alpha 500.0 500.0 500.0 500.0 hemihydrate Organic binder Vinylacetate/ — 40.0 40.0 40.0 ethylene copolymer⁽¹⁾ Vinyl acetate/ 60.0 — —— vinyl versatate copolymer⁽²⁾ Water repellent Silicone — — 2.0 — powderSodium 1.0 — — 1.0 stearate White — 100.0 — — cement⁽³⁾ Lightening agentPerlite⁽⁴⁾ 40.0 40.0 40.0 40.0 Water retainer MHPC 3.0 3.0 3.0 3.0Filler Limestone 370.9 291.9 389.9 390.9 Workability agent Talc 20.020.0 20.0 20.0 Additives Thickener, qsp qsp qsp qsp retarder, 1000 10001000 1000 accelerator, colorant ⁽¹⁾stabilized with polyvinyl alcohol;⁽²⁾stabilized with polyvinyl alcohol; ⁽³⁾White Portland cement;⁽⁴⁾Non-water-repellent expanded.

Example 2

Joint compounds were prepared by adding water, in an amount of 42 g ofwater per 100 g of composition, to compositions E, A, B and C ofExample 1. The joint compounds thus obtained were then tested in orderto produce a joint between two paper-faced plasterboards.

Composition A did not give satisfactory results, especially because theuse of cement gives the paste a high pH, thereby causing hydrolysis ofthe starch-based wallpaper adhesive and, consequently, the wallpaperdoes not adhere.

Composition B allowed good application of paint to the joint and goodadhesion of the wallpaper. However, it was very difficult to mix thecomposition, probably because the silicone is very poorly wetted. Suchmixing therefore cannot be carried out on a work site.

Composition C allowed good mixing. However, when applying paint, thejoint absorbed the paint too quickly and the adhesion of the wallpaperto this joint compound was insufficient because of the excessively largeporosity of the joint, which absorbed an excessive amount of adhesive.

Composition E, which met all the formulation criteria of the invention,mixed normally and gave good bonding, and the binder created asufficiently thick film for application of the paint or for bonding ofthe wallpaper. The alpha-type plaster used made it possible to reducethe water required and, consequently, the shrinkage on drying. Theperlite made the joint compound easy to rub down and also reduced theshrinkage. This joint compound was therefore satisfactory from allstandpoints.

1. A joint compound composition comprising: a) 50 to 60% of calciumsulphate hemihydrate; b) 5 to 15% of an organic binder in powder form;and c) 0.05 to 0.2% of a water repellent selected from the groupconsisting of oleic acid, stearic acid and their alkali metal oralkaline earth metal salt.
 2. The joint compound composition accordingto claim 1, which further includes: d) 1 to 10% of a lightening agent.3. The joint compound composition according to claim 1, wherein thecomposition comprises 5 to 10% of the organic binder; 0.07 to 0.15% ofthe water repellent; and 3 to 7% of a lightening agent.
 4. The jointcompound composition according to claim 1, wherein the calcium sulphatehemihydrate is of the alpha form.
 5. The joint compound compositionaccording to claim 1, wherein the organic binder is selected from thegroup consisting of copolymers of vinyl esters and of ethylene monomers,polyacrylics, vinyl acetate/acrylic copolymers, styrene/acrylic andstyrene/butadiene copolymers, vinyl acetate/vinyl versatate/acrylic andvinyl acetate/vinyl versatate/vinyl maleate terpolymers, acrylicterpolymers and blends thereof.
 6. The joint compound compositionaccording to claim 2, wherein the lightening agent is perlite.
 7. Thejoint compound composition according to claim 2, wherein the lighteningagent is non-water-repellent expanded perlite.
 8. The joint compoundcomposition according to claim 1, wherein the composition is in the formof a powder.
 9. The joint compound composition according to claim 1,wherein the composition is in the form of a powder composed of particleshaving a diameter of at most 200 microns.
 10. The joint compoundcomposition according to claim 1, wherein the water repellent isselected from the group consisting of oleic acid and its alkali metal oralkaline earth metal salt.